The prior art contains certain devices adapted to act as one-way valves (check valves) permitting liquid to flow in one direction only along a pipe or conduit. More specifically, the following two patents are considered relevant to the present invention:
U.S. Pat. No. 4,324,506, issued Apr. 13, 1982 to Steinke. PA0 U.S. Pat. No. 1,861,397, issued May 31, 1932 to Khun.
Both of these prior patents incorporate a structure in which a closure gate is adapted to be swung to the closed position by the action of the rising level of liquid on one or more floats. The floats are connected to one end of a simple lever arrangement, the other end of which is the closure gate.
The more relevant of these two prior patents is Khun, who shows a check valve for sewage pipe in which relatively large float members are pivotally connected through a crankshaft arrangement to a closure gate. The weight of the floats maintains the closure gate in the open position when the water level in the valve is low, and the upward buoyant effect of rising water on the floats allows the closure gate to close by swinging downwardly under its own weight.
Both of these prior patents, however, suffer from certain disadvantages which it is an aspect of the present invention to overcome. In the first place, the provision of pivoted or hinged connections between various components always represents a danger, in that rust or extraneous materials could become lodged in and around the pivot region, thus inhibiting the action of the gate, possibly with disastrous effects.
In this connection, it is important to understand that most municipal and government regulations pertaining to sewage and plumbing do not permit any valve of this kind to stay closed on a permanent basis, due to the fact that, without circulation of air, there is a danger of gas accumulation which could lead to explosion. It is thus important for the valve to be naturally biased to the open position, except when it is activated to close upon build-up of the liquid level due to reverse flow. Thus, a problem with the prior art devices described above is that the hinged or pivotal connection between the floats and the closure gate could become clogged or coated in such a way as to prevent the proper functioning of the valve.
Yet another danger exists with the prior art devices, namely that, in the event that the floats become disconnected from the closure gate arrangement, the latter would naturally seek a closed position under the action of gravity. This would take place even at low liquid levels, which would lead to the danger of gas build-up and explosion.
Yet another disadvantage of the prior art arrangements is the fact that, being of very large size, it is necessary to go to some trouble in order to gain access to the interior for inspection.